Photocatalyst- and transition-metal-free α-allylation of N-aryl tetrahydroisoquinolines mediated by visible light

A convenient and efficient alpha-allylation of N-aryl tetrahydroisoquinolines has been achieved. This transformation can be realized under only visible light irradiation without the aid of transition metals or photocatalysts. The mechanism involves a novel in situ-generated electron-donor-acceptor (EDA) complex between the N-aryl tetrahydroisoquinolines and an allyl or a benzyl bromide. Irradiation with purple light triggered single-electron transfer (SET) from the N-aryl tetrahydroisoquinolines to the allyl or benzyl bromide of the EDA complex, inducing the formation of the corresponding allyl or benzyl radical and the subsequent radical-radical coupling. This approach represents the first example of a photocatalyst- and transition-metal-free alpha-allylic and benzylic functionalization of N-aryl tetrahydroisoquinolines.